Richard Harrison wrote:
Ian White, GM3SEK wrote:
"That statement bears no physical relationship to how this instrument
actually works---."

We`ve been through detailled explanations of how a Bird works. Cecil did
not need to do another. The wattmeter takes actual samples of the
voltages and currents at any single point on the coax. These are
representative of the powers which are moving toward the load and away
from the load. Careful calibration allows indicarions in watts.

An electric current through a speedometer is calibrated to indicate
miles per hour. It works. So does the Bird Wattmeter.

The difference is that nobody is trying to create a complete distortion
of the way a speedometer works.

I am not criticizing the Bird 43 at all. I own one, and use it
regularly. It is a clever concept, well executed and with lots of good
features.

My objection is against the "other Bird 43" - not the real hardware, but
a piece of vaporware that is called a "Bird" but only exists in
someone's imagination. Somehow, this imagined instrument can truly
*measure* how much power is flowing in the forward and reverse
directions, and those measurements can be used to "prove" some point
about transmission line theory.

The real-life Bird 43 cannot do that. Its indications of "forward and
reflected watts" are only printing on the meter scale. They come from
calculations that are totally dependent on transmission line theory, so
they cannot be used to prove anything *about* that subject.

You cannot prove a theory by using evidence that depends on the theory
you're trying to prove. That is just simple logic.

The real Bird 43 is a good and useful piece of test equipment... but
nobody should buy that "other" one.


--
73 from Ian G/GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek